1. Field of the Invention
This invention relates to the color diffusion transfer photographic process, and more particularly, to a novel neutralizing system for use in color diffusion transfer photographic elements.
2. Description of the Prior Art
It is well known that a neutralizing layer is used for arresting development and stabilization of images in photosensitive materials for the color diffusion transfer process. Furthermore, it is well known to form a neutralizing system to prevent too fast a neutralization by combining a neutralizing layer and various timing layers as illustrated in Research Disclosure, No. 12331 (No. 123, July, 1974). In particular, U.S. Pat. No. 3,753,764 describes the use of acetyl cellulose in such a timing layer. However, it is pointed out in U.S. Pat. No. 4,029,849 that the use of acetyl cellulose in a timing layer is accompanied by such difficulties as the storage stability at high temperature and high humidity is reduced, the acetyl cellulose is difficult to hydrolyze with alkali to prolong the neutralization time period, and the maximum and minimum transferred optical densities increase. U.S. Pat. No. 4,029,849 describes the use of a maleic anhydride copolymers together with acetyl cellulose for overcoming these difficulties, however, even if acetyl cellulose is used together with styrene-maleic anhydride copolymer, which is described in U.S. Pat. No. 4,029,849, the storage stability is still insufficient and hence further improvement is desired. Still, because a maleic anhydride copolymer has insufficient compatibility with acetyl cellulose, the stability of the coating composition containing such a copolymer is low and the transparency of the coated layer is poor.
U.S. Pat. No. 4,029,849 discloses mixing acetyl cellulose with copolymer containing a maleic acid monomethyl ester comonomer but the copolymer contains maleic anhydride which makes the copolymer essentially different than the copolymer of this invention, the essential feature of which is that it does not contain maleic anhydride and contains 10 to 80 mol% of a half ester of maleic acid as the comonomer component.
If the transparency of a timing layer is not good in a film unit wherein a light-sensitive element is exposed through the timing layer, the sensitivity and resolving power of the unit is low.